The first thing you should do in Windows 8.1 is set your tethering connection as metered. This will tell Windows to not download any non-critical updates, Windows Store apps may restrict their data usage (mine kept crashing), and offline file sync via OneDrive should stop. It essentially slams the brakes on Windows' major background data vampires.
To go metered, click on the network icon in the bottom right hand side of the taskbar. A charms bar will pop out with a list of all your connections. Right-click the tethering connection and select Set as metered connection .
You can also tweak a few other things to take advantage of the metered setting. Open the Settings app in the Modern UI by tapping the Windows logo key + "C". Then go to
Settings > Change PC settings > OneDrive > Metered connections.
For maximum bandwidth savings, you'll want to make sure all of the options there are set to Off .
Next, back to the main menu in the Settings app and select PC and devices > Devices . Scroll down and make sure Download over metered connections is set to Off . Then go to
Search and apps > Search and make sure everything under Metered connections is also turned off, unless you want search suggestions from Bing while searching your PC over a tethered connection.
Choose your browser
There are two browsers you can choose to reduce your data usage while tethering: Chrome and Opera.